1. Field of Invention
The present invention relates to a vacuum control system for keeping degree of vacuum accurate and constant in an instrument requiring vacuum (decompression), and specifically to a vacuum control system suitable for a vacuum degassing apparatus for removing dissolved gas from liquid isolated with a gas permeation diaphragm by reducing inside pressure of a vacuum vessel being fitted into a precision analytical instrument and having the gas permeation diaphragm by means of an exhaust vacuum pump, and a vacuum degassing apparatus employing the vacuum control system.
2. Description of the Related Art
Degassing apparatuses for removing or reducing dissolved gas in a liquid (hereinafter, this is referred to as “degassing”) were conventionally widely used to secure stability or measurement accuracy of precision analytical instruments using a liquid. Since most of them have a basic structure that gas dissolved in a liquid is removed through the gas permeation diaphragm by allowing the liquid to flow in one side (for example, an inside of a degassing tube) isolated with the gas permeation diaphragm such as a degassing tube, which is provided in the vacuum vessel, having a property of transmitting a gas and not transmitting a liquid while decompressing the other side (for example, an inside of a vacuum vessel), they accompany a vacuum control system constituting a constant vacuum field.
In such type of conventional vacuum control system, in order to keep the inside pressure of a vacuum vessel constant, methods of monitoring the inside pressure of the vacuum vessel and intermittently activating a vacuum pump, or activating a switching valve provided in the vacuum exhaust path to adjust the vacuum condition, etc. are used.
On the other hand, in a vacuum degassing apparatus used for an analytical instrument, generally, a diaphragm type vacuum pump is widely used as the exhaust vacuum pump. If using the diaphragm type vacuum pump, since the vaporized components degassed into the vacuum vessel through the gas permeation diaphragm are compressed, condensed and generate dew condensation in a pump head to deteriorate the performance of the vacuum pump, various improvements have been contrived conventionally. For example, such improvements are disclosed in Japanese Unexamined Patent Application Publication No. 2001-87601, 2000-102702, Heisei 8-024509, 2000-162100 and the like.